This invention relates to an antiskid apparatus for vehicles adapted to prevent the wheels of an automotive vehicle from locking up and skidding on a road surface when the hydraulic pressure brake system of the vehicle is actuated.
A first aspect of the present invention relates to an antiskid system of an automotive vehicle, especially the actuator of the antiskid system. More particularly, the first aspect of the invention relates to a so-called "closed-type" actuator of a vehicle antiskid system equipped with a cut-off valve for selectively cutting each hydraulic pressure line connecting the vehicle brake master cylinder and a respective wheel brake cylinder into a hydraulic pressure line section on the brake master cylinder side and a hydraulic pressure line section on the wheel brake cylinder side; an accumulator for accumulating power hydraulic pressure above a maximum value of brake fluid pressure at which the vehicle wheels approach a state near lock-up; a piston moved in one direction by the hydraulic pressure in the hydraulic pressure line section on the wheel brake cylinder side and moved in the opposite direction by the power hydraulic pressure to close and open the respective cut-off valve and, moreover, to increase and restore the volume of the hydraulic pressure line section on the wheel brake cylinder side by such reciprocating motion; and a directional control valve installed in a power hydraulic pressure line connecting the accumulator with a fluid chamber formed on one side of the piston for being supplied with the power hydraulic pressure, the valve operating to discharge the power hydraulic pressure from the fluid chamber when the vehicle wheels approach the lock-up state and to supply the fluid chamber with the power hydraulic pressure under all other conditions.
In the above-described conventional closed-type actuator, no means whatsoever are interposed between the accumulator and the directional control valve. This means that though the power hydraulic pressure in the fluid chamber is discharged when the wheels approach the lock-up state due to actuation of the brake, the fluid chamber is supplied through the directional control valve with the high power hydraulic pressure in the accumulator under all other conditions regardless of whether the brake is being actuated or not.
A second aspect of the present invention relates to a vehicle antiskid apparatus equipped with a first valve installed in a hydraulic pressure line connecting the vehicle brake master cylinder and a respective vehicle wheel brake cylinder for selectively cutting-off the hydraulic pressure line into a hydraulic pressure line section on the brake master cylinder side and a hydraulic pressure line section on the wheel brake cylinder side; an (e.g., gas spring-type) accumulator for accumulating power hydraulic pressure generated by a power-driven pump; a hydraulic pressure control piston moved in one direction from a rest position by the hydraulic pressure in the hydraulic pressure line section on the wheel brake cylinder side and moved in the opposite direction to the rest position by the power hydraulic pressure to close and open the first valve and, moreover, to increase and restore the volume of the hydraulic pressure line section on the wheel brake cylinder side by such reciprocating motion; and a second valve operable when the wheels are rotating noramally for applying the power hydraulic pressure to the hydraulic pressure control piston in order to situate the hydraulic pressure control piston at the rest position by moving the piston against the hydraulic pressure of the hydraulic pressure line section on the wheel brake cylinder side, and operable when the wheels are about to lock for discharging the power hydraulic pressure from the hydraulic pressure control piston in order to move the hydraulic pressure control piston in the one direction by the hydraulic pressure of the hydraulic pressure circuit section on the wheel brake cylinder side.
An example of a prior-art apparatus of this type is described in the specification of U.S. Pat. No. 3,722,960. This conventional apparatus is adapted to apply the high power hydraulic pressure prevailing in the accumulator directly to the hydraulic pressure control piston when the wheel are rotating normally, and to discharge the power hydraulic pressure from the piston when the wheels are about to lock.
A third aspect of the present invention relates to an antiskid apparatus of the type which conventionally includes a plurality of cut-off valves for cutting a plurality of brake fluid pressure circuits, which connect the master cylinder and respective ones of the wheel brake cylinders, into a section on the master side and section on the wheel side; a single hydraulic pressure pump for feeding, under pressure, a working fluid contained in a reservoir; a single pressure regulating valve which, in dependence upon the master cylinder hydraulic pressure, controls the hydraulic pressure fed from the hydraulic pressure pump to obtain a power hydraulic pressure of a higher value; a plurality of hydraulic pressure control pistons which receive the power hydraulic pressure obtained by the pressure regulating valve on one side thereof and brake fluid pressure on the other side thereof for opening and closing respective ones of the cut-off valves on this other side and for controlling the hydraulic pressure on the wheel side in respective ones of the brake hydraulic pressure lines; and a plurality of directional control valves for effecting supply and discharge of power hydraulic pressure to and from respective ones of the hydraulic pressure control pistons in dependence upon whether or not the wheels of the vehicles are in a state near lock-up.
In the above-described apparatus, the cut-off valves, reservoir, hydraulic pressure pump, hydraulic pressure control pistons and directional control valves are assembled together and the resulting assembly is mounted on the vehicle. In the assembly before it is mounted, the pump is driven, a pressure equivalent to the master cylinder hydraulic pressure is applied to the pressure regulating valve and a pressure equivalent to the brake fluid pressure is applied to the other side of each hydraulic pressure control piston, under which condition the directional valves are actuated. When this is done, the hydraulic pressure control pistons travel their full stroke. By repeating this operation in a short time, therefore, a large quantity of working fluid can be made to flow from the hydraulic pressure pump toward the reservoir. This enables all of the air in the power hydraulic pressure system extending from the hydraulic pressure pump to the reservoir to be vented quickly and easily.